1. The Field of the Invention
This invention relates to a method of making an alloy comprising hard particles comprising titanium carbide dispersed in a predominantly metal matrix, and to the resulting alloy itself.
Alloys of the aforementioned kind are hereinafter referred to as titanium carbide metal matrix alloys; as known hitherto they are generally in the form of a high concentration of titanium carbide particles dispersed in a metal matrix such as ion.
2. Description of the Related Art
Titanium carbide metal matrix alloys are used in, for example, the following applications:
(i) Hard Facing
A hard, wear-resisting layer of the alloy is applied to a substrate metal, by depositing it from a thermal spray powder comprising the metal matrix alloy in powder form, or from a welding electrode made from the metal matrix alloy.
(ii) As an Alloying Component
Titanium carbide particles are introduced into an alloy melt by adding the metal matrix alloy, either in bulk (e.g. lump) form, or by feeding in a cored wire containing the metal matrix alloy in powder form.
(iii) As a Powder Metallurgical Product
Hard composite products are made by powder metallurgical techniques from a mixture of powdered titanium carbide and a powdered metal or alloy which is to serve as the matrix in the product.
The following methods may be used for making titanium carbide metal matrix alloys:
(a) Vacuum Carburization
Fine powders of titanium dioxide and carbon are thoroughly mixed and then reacted at high temperature in a vacuum induction furnace. The resulting titanium carbide is then cooled, comminuted, and mixed with the matrix material, and is subsequently formed into a composite product by a powder metallurgical technique. This method is used industrially.
Although the titanium carbide produced by the carburization step can be of high purity, the vacuum induction process is expensive, and the comminution step can result in the introduction of undesirable impurities on the surfaces of the titanium carbide particles.
(b) Carburization within the Metal Matrix
It is known that if one forms a high carbon ferrous melt containing one or more carburizable alloying metals such as titanium, the respective carbide(s) can be precipitated. While held in the melt, those particles can grow to an undesirable extent, especially when the carbide concentration is high.
European Patent Specification No. 0212435 Al suggests a method of making carbide master alloys involving carburizing ferroalloys in the solid state, with the intention that the resulting carbide particles should be fine. Details of the carburisation process are not given.
(c) Direct Carburization of Titanium Powder
This method has been used industrially. It involves reacting a mixture of powders of titanium metal and carbon. The resulting product is a sintered titanium carbide mass, which has to be broken down to a fine particle size, and then mixed with metal matrix powder, to be formed powder metallurgically into a metal matrix composite product. Powdering the sintered titanium carbide mass to the required degree is difficult, and leads to the titanium carbide picking up impurities. Also, the titanium powder reactant is expensive.